A sputtering apparatus generates a plasma, and causes ions generated by the plasma to collide with a target so as to expel a target material and make it adhere to a substrate, thereby forming a film. Of such film formation processing apparatus, an apparatus called a magnetron type apparatus generates a magnetic field parallel to a target surface by a cathode magnet (magnetron unit) placed on the rear surface of the target. Since this magnetic field crosses the electric field between the target and the substrate, electrons emitted from the target are confined near the target to increase the plasma density. For this reason, the film formation rate in a magnetron type sputtering apparatus strongly depends on the strength of the electric field and leakage magnetic field formed on the target.
The strength of a magnetic field from the magnetron unit placed on the rear surface of a target, in particular, has a significant effect on plasma density and influences the film thickness distribution on a substrate. In general, as the strength of the magnetic field increases, the plasma density increases. This raises the sputtering rates and hence increases the film formation rate at a particular location on the substrate.
Under these circumstances, there have been proposed, as methods of modifying the film thickness distribution on a substrate, a method of implementing adjustments by changing the magnetic circuit for forming a magnetic field by increasing/decreasing the strength of a magnetic field (see patent references 1 to 3):
Patent Reference 1: Japanese Patent Publication NO. 7-26202 (FIG. 1)
Patent Reference 2: Japanese Patent Laid-Open No. 9-118980
Patent Reference 3: Japanese Patent Laid-Open No. 3-75369 (FIG. 5)